1. Field of the Invention
This invention relates to a fluid material discharge device and discharge method. In particular, this invention relates to a dense fluid material discharge device and discharge method, regarding a paste dispenser used to apply a paste, of which the bonding paste used for bonding a semiconductor chip to a lead frame is representative.
2. Description of the Related Art
In electronics fields, a dispenser having as the principal component a discharge device 1, comprising a fluid material holder 2 and a nozzle 3 connected to the fluid material holder 2 as shown in FIG. 1, is known for a method to supply paste for use in bonding to, for example, a lead frame.
In the discharge device of FIG. 1, often the paste in the fluid material holder 2 is pushed out from the tip of the nozzle 3 by the force of pressurized gas supplied from a pressurized gas supply aperture 4.
Normally dispensers use cylindrical-shape needle nozzles with hollow interiors; discharge from the tip is controlled by setting the amount of pressure applied to the syringe interior, which is the fluid material holder, and the time duration of pressure application.
When applying a fixed amount of a paste containing silver filler or similar using a dispenser, if a widely used needle nozzle is employed, inadequate discharge (that is, discharge in which an inadequate amount or no amount is discharged) sometimes occur due to liquid clogging within the needle nozzle, and due to the fact that air bubbles which have remained owing to inadequate defoaming, contract when the paste is pressurized, and absorb the pressure applied.
For paste which is difficult to control owing to poor flowability, what is called a precision nozzle, with a conical taper formed in the interior of the nozzle, has been commercialized; though flowability is improved somewhat, the cost is prohibitive at some 20 times or more that of a conventional needle nozzle, and in addition high positioning precision with the object for application is required, so that the problems in question are not completely alleviated.
For highly viscous paste, a screw or other component is incorporated between the syringe and the nozzle, in a certain commercialized product type which forcibly discharges the fluid material; this is also expensive, however, and maintenance is required.
Japanese Utility Model Publication No. S59-36306 discloses a discharge device 5 which, as shown in FIG. 2, comprises a fluid material holder 6; nozzle 7; core wire 8 somewhat smaller than the inner diameter of the nozzle tip, inserted into the nozzle; and spring 9, enabling the core wire 8 to move vertically within the nozzle 7.
In this device, the fluid material is not discharged outside the nozzle by pressure, but is discharged by the action of the following cycle.
(1) Under the action of the spring 9, a portion of the core wire 8 in the nozzle moves outside the nozzle, and by this means the fluid material is extracted from the nozzle.
(2) When the nozzle 7 is pressed against an adherend (in this specification, the object onto which the fluid material is caused to adhere is called the adherend), the fluid material between the nozzle tip and the core wire 8 is scraped away, forming a flat shape on the adherend.
(3) Next, as the nozzle 7 is withdrawn from the adherend, the fluid material on the adherend retains a flat shape and remains on the adherend.
(4) Under the action of the spring 9, a portion of the core wire 8 within the nozzle again moves outside the nozzle, and by this means the fluid material is extracted. In other words, the above step (1) is repeated.
The above invention has as an object the ability to cause the fluid material remaining on the adherend to be flat rather than hemispherical, so that during bonding the chip or other object to be bonded can be fixed in a normal position.
However, this invention makes no suggestions regarding the prevention of inadequate discharges.
Also, because the construction of the spring or other parts in the device is complex, it is difficult to further provide other means for the discharge of fluid material, such as providing a path for intake of pressurized gas.
In the above publication, as indicated by the expression “core wire somewhat smaller than the inner diameter of the nozzle tip”, in the above process (2), the gap between the nozzle tip and the core wire 8 must be made small in order to perform the scraping-off.
The amount of fluid material discharged is greatly influenced by the gap, the viscosity and thixotropic properties of the fluid material, the speed of the above cycle, etc.; the viscosity and thixotropic properties of the fluid material fluctuate according to variation in the quality of the fluid material, the temperature of the fluid material, and other factors, and so there is the problem that, in order to maintain a constant fluid material discharge amount while keeping production speed in a fixed range (holding constant the above cycle), the size of the core wire 8 and size of the nozzle must frequently be changed in a delicate manner.